In conventional gravity separators, differences in the specific gravities of the different components of the feed material are used to accomplish separation. More specifically, a stream of feed material is fed onto a downwardly sloping surface, which may be an inclined plane, cone, or spiral, where it flows under the influence of gravity. The higher specific gravity particles settle near the bottom of the stream while the light materials accumulate near the top. While typically the materials settling near the bottom of the stream represent the valuable part of the ore, that is not always the case. In any event, as is well known in the art, various separating means may be employed to separate the materials settling at the bottom of the stream from those near the top.
In the case of some metallic ores, it is highly beneficial to combine gravity separation with magnetic separation, as disclosed in commonly owned U.S. Pat. No. 4,565,624, the contents of which are incorporated herein by reference in their entirety. This patent discloses a gravity-magnetic ore separator for concentrating magnetic or weakly magnetic minerals having a relatively high specific gravity and utilizes magnetic and gravitational forces acting co-directionally. Under the influence of both magnetic and gravitational forces, magnetic particles are collected more efficiently at the bottom of the sloped surface thereby enhancing recovery and reducing costs.
The patent specifically describes gravity-magnetic separators constructed by modifying conventional gravity separators, such as Reichert cone concentrators or Humphreys spirals. The Humphreys spiral, introduced in 1943, is typically made of cast-iron which shields the feed material from the magnetic forces This problem is emphasized in U.S. Pat. No. 4,565,624 (see col. 7, lines 35-41) wherein it was concluded that it would be impossible to retro-fit a cast-iron spiral with magnets to achieve satisfactory gravity-magnetic separation without first replacing portions of the iron spiral with a non-metallic material. However, the high cost of such replacement has proved an impediment to the modification of the cast-iron Humphreys spiral as a gravity-magnetic separator.
Accordingly, it is an object of the present invention to provide cost effective means for modifying existing gravity separators of the type having a sloping surface made of metal to make them gravity-magnetic separators.
It is a further object of the invention to provide such gravity-magnetic separators without, however, requiring the replacement of portions of the sloping surface with non-metallic material.